The Öglunda caves were formed underneath massive fallen stone blocks, and there are also free-standing pillars of dolerite. These types of hollows, caves and pillars can be found all along the dolerite slopes around Billingen.
Dolerite is an igneous rock, which means that it was created from magma from beneath the Earth’s crust. Around 300 million years, magma forced its way up through cracks in the surrounding hostrocks. When the hot magma cooled and solidified as dolerite, it cracked, usually forming hexagonal pillars, but also forming much longer cracks. This is what gave rise to the distinctive appearance of the mountain slopes, with their pillars, clefts, hollows and caves.
Remember that this is hazardous terrain, so keep a close eye on children and keep dogs on a leash!